Adhesives, applications joining

SBR adhesives are used in applications where low stress but high flexibility and resistance to shock are needed. If ageing is critical, SBR adhesives should not be used. SBR adhesives have relatively low surface energy and therefore can be used as general-purpose adhesive to join several substrates. 

Since the adhesives only crosslink at specific wavelengths, the parts to be joined can be premounted and fixed with a high degree of positional accuracy under normal workplace conditions. Quality control can also be realized (proof of adhesive application, positional correction) without affecting the adhesion of the bond. 

The percentage of solids in the dispersion adhesives is 35-55%, in some cases as much as 70%, the rest is water, which after the adhesive application must either be completely evaporated (ventilation time) or diffuse into the joined parts (wood, textiles, concrete, foams, leather). The film formation temperature in types containing plasticizers and flexibilizing additives is lower than in types that are free of plasticizers. Additives, so-called high boilers (ethyl glycol, ethyl glycol acetate, ethylhexanol), are used to bring the film formation temperature down. 

Setting time Period of time in which the adhesive, after joining, reaches the degree of crosslinkage required for the application-related stress. 

Epoxies, reinforced with fibers, are used for struetuial applications and they are also used as an adhesive for joining composite structures or attachment of metals. For these purposes epoxy usefulness is severely limited by its susceptibihty to water permeation and beeause epoxies lack toughness. Beeause of the eommeicial importance of epoxy, it is of interest to develop a greater understanding of the mechanisms involved in toughening (12). 

The adhesive pellets are processed in an extruder at 170-210°C [66]. Addition of 0.5-1.0% of a carbodiimide is recommended for TPU polyester adhesive applications. The role of carbodiimides will be discussed later. Even though polyesters are more resistant to oxidation than are polyethers, antioxidants are often added to prevent chain scission. In a shoe cap application, the adhesive web can be applied to a substrate on one side and a release liner on the other side. The bond is then cooled and cut into the proper shape. The shoe cap may be assembled by first heating the TPU adhesive to the proper temperature, using infrared lamps. The cap is then joined with the second substrate, followed by pressure and cooling, until crystallization is complete. 

Structural adhesives, which have found applications in the aircraft, automobile, construction, and electronics industries, can alleviate the problems caused by stress concentration and provide additional advantages to the bonded system (see the introductory chapter of this book). Many adhesive applications involve the joining of high-modulus substrates such as metals, wood, composites, and plastics where the adhesive provides a medium for stress transfer between the substrates. The adhesive layer improves the vibrational damping capabilities of the system. Although the bonded system is susceptible to property degradation by environmental exposure, the adhesive layer increases the corrosion resistance when dissimilar metals are bonded. 

Adhesive application the application and distribution of an adhesive over the surface to be joined. 

In the second case, the robot can also join the component after the adhesive application. It must be noted that this type of production has longer cycle times than application with a moving nozzle. Certainly, the number of robots and handling robots is lower. This is ultimately a question of economics, which should be clarified at an early stage of the project. 

Although a fully automatic bonding process including adhesive application and joining of adherends is possible, it is hard to check visually the mixture condition, the applied amount of adhesive, and its application patterns. Imaging technologies are, of course, possible to use recently. However, there are several problems in terms of cost and accuracy so far. A combined process of automation and manual work is very efficient for such situations. For instance, adherend joining can remain a manual operation to check the adhesive condition mentioned above, which is helpful to avoid defects. 

An advantage of manual operation is the availability of a sequential process from adhesive mixture to pressurization. This whole process can be carried out continuously by one person. On the other hand, a parallel process is dangerous because the pot life of the adhesive applied to many queuing parts can be attained if the production line stops before the joining process. Since automation needs a parallel process, a waiting system for the adhesive application, which is activated when the following processes consume too much time, has to be installed. 

In current rolling stock, adhesives are mainly utilized to join interior equipments. O Table 47.1 summarizes typical adhesive applications for rolling stock use (Suzuki 2006, 2009). O Figure 47.3 shows the share ratio of adhesive types and purposes in the cases of suburban electric cars and Shinkansen cars (Suzuki 2006, 2009). 

Lamination Inks. This class of ink is a specialized group. In addition to conforming to the constraints described for flexo and gravure inks, these inks must not interfere with the bond formed when two or more films, eg, polypropylene and polyethylene, are joined with the use of an adhesive in order to obtain a stmcture that provides resistance properties not found in a single film. Laminations are commonly used for food applications such as candy and food wrappers. Resins used to make this type of ink caimot, therefore, exhibit any tendency to retain solvent vapor after the print has dried. Residual solvent would contaminate the packaged product making the product unsalable. 

In joining reinforced thermosetting pipe it is particularly important that the pipe be cut without chipping or cracking it. It is also important to sand, file, or grind any mold-release agent from the surfaces to be cemented. Joints are built up layer by layer of adhesive-saturated reinforcement by following the manufacturer s recommended procedure. Application of adhesive to the surfaces to be joined and assembly of these surfaces shall produce a continuous bond and provide an adhesive seal to protect the reinforcement from attack by the contents of the pipe. Unfilled or unbonded areas of the joint are considered defects and must be repaired. 

The primary challenge facing adhesive bonding of metals is to obtain sufficient durability of a bonded structure. Initial bond strength in metal-polymer adhesive joints is almost invariably excellent. Challenging the application of adhesives in polymer-polymer joining, however, is the problem of obtaining a joint that is... 

The dry adhesive films on the two substrates to be joined must be placed in contact to develop adequate autoadhesion, i.e. diffusion of polymer rubber chains must be achieved across the interface between the two films to produce intimate adhesion at molecular level. The application of pressure and/or temperature for a given time allows the desired level of intimate contact (coalescence) between the two adhesive film surfaces. Obviously, the rheological and mechanical properties of the rubber adhesives will determine the degree of intimacy at the interface. These properties can be optimized by selecting the adequate rubber grade, the nature and amount of tackifier and the amount of filler, among other factors. 

Nitrile rubber adhesives. The main application corresponds to laminating adhesives. PVC, polyvinyl acetate and other polymeric films can be laminated to several metals, including aluminium and brass, by using NBR adhesives. NBR adhesives can also be used to join medium-to-high polarity rubbers to polyamide substrates. The adhesive properties of NBR rubbers can be further improved by chemical modification using polyisocyanate or by grafting with methyl methacrylate. 

Construction. CR adhesives find uses in countertops and panel fabrication for curtain walls and partitions. Other large volume applications are the joining of... 

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